Method of carburizing one side only of relatively short tubular parts



Dec. 17, 1946. E. (5. DE CORIOLIS 2,412,302

METHOD OF CARBURIZING- ONE SIDE ONLY OF RELATIVELY SHORT TUBULAR PARTS Filed Aug. 17, 1944 v v v v v N x FiG-l Zsmaentor E.G. a e-Corl oll s $4 gig Patented Dec. 17,1946 4 w 2,412,802-

UNITED STATES PATENT OFFICE" METHOD or CARBURIZING ONE SIDE ONLY OF RELATIVELY snon'r TUBULAR rAn'rs Ernest G. de Coriolis, Toledo, Ohio, assignor to Surface Combustion Corporation, Toledo, Ohio, a corporation of Ohio Application August 1 7, 1944, Serial No. 549,885 3 Claims. (011148-17) 1 2 This invention relates to Ways and means for leng h of the rough finished machine Part. In heat treating tubular machine parts, such aspis- Fig. 2, reference numeral I may be said to repreton pins for internal combustion engines, in a sent apiece of tubing of piston pin length and manner to produce a wear resisting surface or 2 a piece of tubingof stock length, it being noted difiusion alloy case on one side without'also:prothat the latter is many times longer than the ducing a similar case on the opposite side so that former. 1 the last'mentioned sidemay be left relatively soft In accordance with the present invention the to impart toughness to the part. tubing is passed through a furnace chamber Various schemes have heretofore been proposed wherein it will be heated to case forming temfor producing piston pins which are case hard- 10. perature in the. presence. of a carburizing gas. ened on the outside and soft on the inside. One The formation of the desired case is a matter scheme involves carburizing a solid rod of piston of hours, say, about six hours, and the furnace pin length and then, before quenching to harden, will therefore be a relatively long affair, say, boring the necessary axial hole in the rod. This about 40 feet. The tubing is passed through the method is obviously wasteful of steel. Another furnace in end to end relation as a string of scheme involves starting with tubular pieces of greater length than the furnace so that the ends piston pin length, placing a number of these of the string will extend beyond both ends of pieces on a spindle type fixture having cap means the furnace whereby to permit a protective gas at its ends for clamping the pieces tightly toto be passed through the string to prevent infilgether at their ends with the object in view of tration of carburizing gas through the joints of making the interior of the assembly gas-tight, the string from having any objectional effect on and then exposing the assembly to the action of the inside of the tubing. It is, of course, desira carburizing gas. However, aside from the trouable that the joints of the string shall be relaole involved in handling the pieces in this way tively gas-tight for the double purpose of preit is extremely difficult in practical operation to venting objectional leakage of gas either into or make the joints between the pieces sufficiently out of the string. The tubes are held in end to gas-tight to entirely prevent carburization of the end relation in any preferred way as by means inner side of the pieces due to infiltration of carof tubular fittings 3 insertable into the ends of burizing gas through the joints. Another scheme the tubes, the fitting preferably having an exteinvolves copper plating the inside of tubular rior circumferential shoulder 4 against which the pieces, but this results in troubles not necessary ends of the tubes abut. to discuss. In the drawing, 5 indicates a string of tubes The present invention aims to provide an im- 6 which are being passed through a case forming proved method for the purpose stated. For a furnace from the left towards the right as viewed consideration of what I believe to be novel and in Fig. l. The furnace comprises a gas-tight my invention attention is directed to the followtunnel l Wherethrough the tubing is passed for ing specification and claims appended thereto. heating to reaction temperature in the presence In the accompanying drawing, of a carburizing gas maintained in the tunnel Fig. 1 is a schematic vertical longitudinal secas by means of a supply pipe 3 leading from. a

tion of one type of continuous case forming fursource of supply 9 of such gas. Spent gas flows nace that may be utilized in the practice of the from the tunnel by way of a vent pipe [0 at present invention. the far end of the tunnel. At the front end of Fig. 2 shows the comparative lengths of a pisthe tunnel is a pair of tube gripping rollers ll ton pin and a much longer piece of tubing from for forcing the tubes through the tunnel. Inside which the pin may be cut. of the tunnel there are suitable supports !2 for Fig. 3 is an axial sectional view of a tubular preventing objectional sagging of the tubes. The connector that may be employed in connection major portion of the tunnel from its tube enterwith the present invention. ing end is surrounded by a combustion chamber Fig. 4 is an axial section of a throttling orifice i3 for maintaining a zone in the tunnel at ease plug that may be employed in connection with forming temperature. The remainder Id of the the present invention. tunnel at the right of the combustion chamber In the practice of the present invention it is constitutes a slow cooling zone for the tubing preferred for reasons presently appearing that emerging from the heating Zone.

the tubing to be treated shall be of the usual A protective atmosphere is maintained in the stock length rather than of the much shorter string of tubes by introducing it thereinto under suitable head into the last tube of the strin by any preferred means as by a flexible conduit or hose l5 leading from a source of supply l6. At the leading end of the string is an orifice plug l! to insure that the pressure of the atmosphere inside of the string shall be slightly greater than that of the ambient. case forming atmosphere which surrounds the string. It will be understood that before the tail end of the string passes into the furnace a new tube will be added and the gas supply hose l5 shifted to the tail end of the new tube and that after the leading tube of the string has emerged from the furnace it is uncoupled from the string and the orifice plug shifted to the new leading end of the string.

It will be understood that after the tubing has been heat treated as described, itis ready to be cut up into appropriate lengths depending on the length of the machine part desired, as piston pins, and that reheating and quenching are required to harden the case produced as said.

If the machine part is such as to require a hardened wear surface on its inside rather than on its outside, the case forming atmosphere will be passed through the string of tubes and the neutral atmosphere will be maintained in the furnace chamber as will now be readily understood.

7 Although the invention has special utility in connection with the carburizing, it is believed to be obvious that the case forming'gas may be something other than a carburizing gas as, for example, a nitriding gas.

From the foregoing it will be readily appreciated that the present invention solves in a relatively simple way the problems heretofore encountered in limiting the production of a diffused alloy case to one side only of a tubular machine part such as piston pins and the like.

What is claimed as new is:

1. The method of producing a diffusion alloy case on one side only of lengths of steel tubing which comprises passing the same through a furnace chamber as a substantially continuous string which extends beyond the ends of said chamber and which is substantially relatively gas-tight at the joints, maintaining a case forming atmosphere in said chamber and a substantially neutral atmosphere in said string, and heating said lengths of tubing to case forming temperature as they pass through said chamber.

2; The method of producing a diffusion alloy case on one side only of lengths of steel tubing which comprises passing the same through a furnace chamber as a substantially continuous string which extends beyond the ends of said chamber and which is substantially relatively gastight at the joints, maintaining one kind of an atmosphere in said chamber and another-kind of an atmosphere. in said string, one of said atmospheres being a substantially neutral atmosphere and the other a case forming atmosphere, and heating said lengths of tubing to case forming temperature as they pass through said chamber. 1

3. The method of producing a oarburized case on the outside only of lengths of steel tubing which comprises passing the same through a furnace chamber as a substantially continuous string which extends beyond the ends of said chamber and which is substantially relatively gas-tight at the joints, maintaining a carburizing atmosphere in said chamber and a substantially neutral atmosphere in said string, and heating said lengths of tubing to carburizing temperature as they pass through said chamber.

ERNEST (3-. DE CORIOLIS. 

